1. Field of the Invention
This invention relates to a plasma or a glow discharge for dissociating one or more gases into reactive and non-reactive ionic and reactive and non-reactive neutral species, and in particular, to improving the power density necessary to dissociate one or more gases for use in a plasma.
2. Description of the Prior Art
Plasma apparatus can be divided into two broad categories, downstream or remote plasma and direct plasma. In downstream plasma, the article(s) are not immersed in the glow discharge, as it is in direct plasma. The result is a somewhat more gentle treatment of the article(s) because high power electromagnetic waves at high frequency are not coupled through the article(s) and there is no heating from direct ion bombardment. In either type of apparatus, it is known in the art to employ some type of plasma for processing one or more article(s).
Typically, one or more reactive gases (such as, oxygen-based gases, or halogen-based gases, including fluorine, chlorine, bromine, or other equivalent gases, as well as gas molecular compounds having one or more oxygen or halogen atoms), are used in combination with other gases due to the highly reactive nature of the reactive gas(es), in a downstream plasma chamber. A problem with these additive gases is that the energy necessary to dissociate some additive gas molecules can be less than that energy necessary to dissociate the intended halogen-based gas molecule. In the discharge zone, the applied energy can be undesirably absorbed by gas molecules other than the reactive gas molecules intended for dissociation.
In the prior art, a power supply producing large amounts of microwave power was typically used to assure dissociation of one or more gases. Much of this power was wasted in recombination away from the one or more articles to be processed by the plasma. Often reactive ions attacked the chamber, or other components, thereby introducing undesirable contamination into the plasma process.
A problem with many gases is that these gas molecules diffuse everywhere, including their diffusion toward the source of the one more reactive gas sources to supply the plasma, thereby contaminating the reactive gas sources. While one could adjust the relative flows of the gases, the mixture would be determined by the diffusion problem, rather than by the most effective mixture for processing the one or more articles to be processed by the plasma.
Another problem with prior art plasma technology for multiple gas sources is that high power was consumed in order to dissociate each gas, and the operating temperatures of the plasma chambers could become sufficiently high to significantly decrease the reliability and/or significantly increase the cooling requirements. Large gas flows for plasma generation also required large amounts of power and could create these same problems.
In view of the foregoing, what is needed is an improved method and apparatus for efficiently dissociating one or more gases into a plasma with a higher power density, and producing reactive and non-reactive ionic species and reactive and non-reactive neutral species from one or more gases, without contaminating the one or more gas sources.